Added Messenger Bot

[Awinja-j]

Healthtools.API currently can only process text messages using twilio and mtech API.

This PR therefore introduces:

• bot/process_bot_query function
• bot/messenger_bot.py and
• views/bot.py

process_bot_query can be used by any bot to do a query search and return a response to the bot. views/bot.py currently uses messenger as default adapter and can be refactored when other bots are added

This task involved:

• Opening/ Having a Facebook account
• Create a Facebook page
• Create a Facebook developer account
• Create a Facebook App on https://developers.facebook.com/
• Configuring messenger to consume a web hook
• refactoring the web hook to fetch data from elastic search by building the process_bot_query that will call run_query function

Relevant Github issue: https://github.com/CodeForAfricaLabs/HealthTools.API/issues/50 and https://github.com/CodeForAfricaLabs/HealthTools.API/issues/47